Method and medical system for determining a link quality of a communication link in such a medical system

ABSTRACT

In a method and medical system for determining a link quality and a link quality margin of a communication link between a programmer device and an implantable medical device of such a medical system, a link quality monitoring circuit of the programmer or the medical device a present link quality and/or link quality margin at reduced signal power using at least one link quality parameter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to cardiac pacing systems and,in particular, to methods and medical systems for determining a linkquality and a link quality margin of a communication link between aprogrammer device and an implantable medical device of such a medicalsystem.

2. Description of the Prior Art

Telemetry communication is normally used between an implantable medicaldevice, such as an implantable bi-ventricular pacemaker or a CRT(Cardiac Resynchronization Therapy) device, and an external orprogrammer workstation to transfer data between the devices, forexample, to transfer IEGM data of the heart of the patient from animplanted device to the programmer or to transfer updating data forupdating a certain setting of the implanted device from the programmerto the implanted device. In telemetry communications, the operationdepends inter alia on used transmission power, interference, reflectingproperties in the near environment, the placement of the RFcommunication unit of the programmer etc. A user of the programmerdevice and/or the pacemaker needs information of the telemetryperformance during such a telemetry communication session, for example,in order to be able to place the RF communication unit at a goodposition. If the RF communication unit is placed at a bad position, theradio link will be unreliable and it might even break down. Today, thelink quality is used to judge whether the RF communication unit isplaced at a suitable location with respect to the patient carrying theimplanted medical device. The link quality is affected by the separationbetween the RF communication unit and the implanted medical device andthe interference, which may arise from external functions (i.e. externaldevice in the environment) but also from device internal functions (e.g.high voltage charge or shocking). Thus, there would be an advantage ifthe user of the programmer and/or the implantable medical device wereprovided with an indication of the link quality.

In U.S. Pat. No. 6,647,299, a solution where a light emitting diode(LED) is used as visible indicator to assist a user to find the desiredtelemetry location of a programmer for a bi-directional communicationlink between the programmer and an implantable medical device. Throughvariations of the visible indicator, the user will know the relativelocation of the programmer and the implanted device. When the programmeris in the proper telemetry position and the signal strength and accuracyhave been confirmed, the light indicator will indicate that a link hasbeen established.

However, a problem with existing link quality indicators is that theyare based on the momentary conditions and do not identify whether thereis a sufficient link quality margin to cope with a sudden increase inthe level of interference. In U.S. Pat. No. 5,843,139 various aspects ofsystem performance in a system including an implantable medical deviceand a programmer are monitored to determine the momentary performance ofthe system. The monitored parameters comprises bit-error rate, signalstrength, signal-to-noise ratio and the presence of local RF noise andnon-telemetry RF-signals.

Therefore, it would be advantageous if a link quality and/or a linkquality margin of a communication link between a programmer and animplantable medical device could be continuously monitored during acommunication session.

Furthermore, there is a need within the art of an efficient, reliableand simple way of testing the link quality and/or link quality margin ofa communication link during a communication session between animplantable medical device, such as a pacemaker, and an external device,such as a programmer workstation.

It is also desirable to provide means for presenting the link quality orthe link quality margin for a user, such as a physician, of theprogrammer device or for a patient in a distinct and intuitive manner.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide methods, medicalsystems including an external programmer device and an implantablemedical device and computer program products for such devices fortesting a link quality of a communication link between a programmer andan implantable medical device.

Another object of the present invention is to provide methods, medicalsystems including an external programmer device and an implantablemedical device and computer program products for such devices fordetermining or calculating a link quality margin of a communication linkbetween a programmer and an implantable medical device.

A further object of the present invention is to provide methods, medicalsystems including an external programmer device and an implantablemedical device and computer program products for such devices forcontinuously monitoring a link quality and/or a link quality margin of acommunication link between a programmer and an implantable medicaldevice to regulate or adjust a signalling power during a communicationsession.

A further object of the present invention is to provide methods, medicalsystems including an external programmer device and an implantablemedical device and computer program products for such devices forcontinuously monitoring a link quality and/or a link quality margin of acommunication link between a programmer and an implantable medicaldevice to obtain a communication link having a high degree ofreliability and a high quality with respect to the data transmission ata low signalling power.

Yet another object of the present invention is to provide methods,medical systems including an external programmer device and animplantable medical device and computer program products for suchdevices for testing the link quality or link quality margin of acommunication link during a communication session between an implantablemedical device and an external programmer device in an efficient,reliable and simple way.

These and other objects of the present invention are achieved by meansof medical systems and methods for such systems, and computer programproducts having the features defined in the independent claims.Preferable embodiments of the invention are characterized by thedependent claims.

According to a first aspect of the present invention, there is provideda medical system comprising an external programmer device and animplantable medical device, wherein a link quality monitoring circuit ofthe programmer is adapted to determine or monitor a link quality of acommunication link during a communication session between the programmerand the implantable medical device, the link quality monitoring circuitfurther being adapted to: instruct a transmitter of a communication unitof the programmer to reduce the signal power from an initial signalpower level according to a predetermined signal power adjustingprotocol; obtain at least one link quality parameter at a present signalpower level from a link quality parameter calculation circuit of theimplantable medical device and/or from a link quality parametercalculation circuit of the programmer at predetermined intervals;determine a present link quality using the obtained at least one qualityparameter; and instruct the transmitter of the communication unit of theprogrammer to adjust the reduced signal power based on the present linkquality and the signal power adjusting protocol.

In a second aspect of the present invention, there is provided a medicalsystem comprising an external programmer device and an implantablemedical device, wherein the link quality monitoring circuit of theprogrammer is adapted to perform a link quality test to determine a linkquality of a communication link during a communication session betweenthe programmer and the implantable medical device. The link qualitymonitoring circuit is adapted to: instruct a transmitter of acommunication unit of the programmer to reduce a signal power from aninitial signal power level according to a predetermined test protocol;obtain at least one link quality parameter at reduced signal power froma link quality parameter calculation circuit of the implantable medicaldevice; determine a present link quality at reduced signal power usingthe obtained at least one link quality parameter; and instruct thetransmitter of the communication unit of the programmer to return to theinitial signal power level when the link quality test has been finished.

According to a third aspect of the present invention, there is provideda medical system comprising an external programmer device and animplantable medical device, wherein a link quality monitoring circuit ofthe implantable medical device is adapted to perform a link quality testto determine a link quality of a communication link during acommunication session between the programmer and the implantable medicaldevice. The link quality monitoring circuit is adapted to: instruct atransmitter of the implantable medical device to reduce a present signalpower from an initial signal power level according to a predeterminedtest protocol; obtain at least one link quality parameter at reducedsignal power from a link quality parameter calculation circuit of theprogrammer device; determine a present link quality at reduced signalpower using the obtained at least one link quality parameter; andinstruct the transmitter of the implantable medical device to return tothe initial signal power level when the link quality test has beenfinished.

According to a fourth aspect of the present invention, there is provideda method for determining a link quality in a medical system comprising aprogrammer device and an implantable medical device. A link quality testis performed to determine a link quality of a communication link duringa communication session between the programmer and the implantablemedical device including the steps of: reducing a signal power level ofa transmitter of a communication unit of the programmer from an initialsignal power level according to a predetermined test protocol; obtainingat least one link quality parameter at the implantable medical device atreduced signal power from the implantable medical device; determining apresent link quality at reduced signal power using the obtained at leastone link quality parameter; and returning to the initial signal powerlevel of the transmitter of the communication unit of the programmerwhen the link quality test has been finished.

According to a further aspect of the present invention, there isprovided a computer program product, directly loadable into an internalmemory of an external programmer device, comprising software codeportions for causing the external programmer device to perform steps inaccordance with the method according to the third aspect.

According to yet another aspect of the present invention, there isprovided computer program product, directly loadable into an internalmemory of an implantable medical device, comprising software codeportions for causing the implantable medical device to perform steps inaccordance with the method according to the fourth aspect.

Hence, the invention is based on the idea of continuously monitoring alink quality and/or link quality margin of a communication link betweena programmer and an implantable medical device during a communicationsession and continuously adapt or adjust transmitted power from asending device, e.g. a transmitter of an RF communication unit of aprogrammer workstation, during a communication session between theprogrammer and an implantable medical device using link qualityparameters at the programmer and/or the implantable medical device.

Thereby, it is possible to cope with changing transmission conditionsand environment during the communication session. The transmitted powercan thus be adjusted or adapted to cope with, for example, a suddenincrease in the level of interference. Since the signalling power isheld at a lowest possible level with respect to the surroundingtransmission conditions, the radiated energy can be minimized and, thus,the distances to other programmer workstations located in the proximityof a first workstation can be reduced. That is, using the presentinvention, a distance between two workstations communicating with animplantable medical device, respectively, can be reduced in comparisonwith the technique used today, i.e. sending at a constant signal powerlevel.

In one embodiment of the present invention, the signal power is reducedfrom said present signal power level if said at least one qualityparameter satisfies at least a first set of predetermined conditionsaccording to said protocol and the signal power is increased from saidpresent signal power level if said at least one quality parametersatisfies at least a second set of predetermined conditions according tosaid protocol.

Moreover, the present signal power level can be maintained at a presentlevel if said at least one quality parameter satisfies at least a thirdset of predetermined conditions and/or the signal power can be increasedto an initial signal power level if at least a fourth set ofpredetermined conditions are satisfied.

Consequently, the power consumption can be reduced the same time as anadequate link quality margin or a link quality satisfying predeterminedconditions with respect to, e.g. an error correction of transmitted dataor re-transmissions of transmitted data packets, can be maintainedduring the communication session. In other words, the signalling poweris continuously held at a level such that predetermined conditionsregarding, for example, error correction of transmitted data and/orre-transmissions of transmitted data packets is satisfied.

According to embodiments of the present invention, a first set ofconditions of the protocol includes: the number of error correctedblocks in the implantable medical device (ECCi) being equal to 0 and thenumber of blocks that could not be corrected in the implantable medicaldevice (CRCi) being equal to 0 for two consecutive intervals ordeterminations; the second set of conditions of the protocol includes:ECCi being higher than 10 and CRCi being higher than 0 and lower than40; the third set of conditions of the protocol includes: ECCi beinglower than 10 and CRCi being equal to or higher than 0 and lower than40; and the fourth set of conditions of the protocol includes: CRCibeing higher than 40 or at a change of an antenna of the communicationdevice.

According to an aspect of the present invention, there is provided amethod for determining a link quality in a medical system comprising anexternal programmer device and an implantable medical device. A linkquality test is performed to determine a link quality of a communicationlink during a communication session between the programmer device andthe implantable medical device, including the steps of: reducing apresent signal power of a transmitter of the implantable medical devicefrom an initial signal power level according to a predetermined testprotocol; obtaining at least one link quality parameter at reducedsignal power from the programmer device; determining a present linkquality at reduced signal power using the obtained at least one linkquality parameter; and instructing the transmitter of the implantablemedical device to return to the initial signal power level when the linkquality test has been finished.

The present invention is hence further based on the insight thattransmitted power from a sending device, e.g. a transmitter of an RFcommunication unit of a programmer workstation, has an equivalent effecton link quality of a communication link between the programmer and animplantable medical device as increasing noise or distance. Therefore,by momentarily reducing the transmitter signal power, the effect ofincreased noise or distance can be simulated or tested and hencemeasured or determined in an effective and simple manner.

According to one embodiment of the present invention, the link qualityparameter calculation circuit may comprise an error detection circuitadapted to detect at least one of the following link quality parameters:forward error correction (FEC), cyclic redundancy check (CRC), or biterror rate (BER).

In a further embodiment of the present invention, the link qualityparameter calculation circuit may comprise a signal strength and noisedetection circuit adapted to detect at least one of the following linkquality parameters: signal strength, or signal-to-noise ratio (SNR).

Furthermore, the link quality parameter calculation circuit may comprisea link delay calculation circuit adapted to calculate a link delay ofthe communication link using a received response message from theprogrammer device or by reading a register of a communication unit ofthe programmer device.

In addition, the link quality parameter calculation circuit may comprisea re-transmission calculation circuit adapted to calculate a number ofre-transmissions of at least one data packet sent from the programmerdevice via the communication link as a link quality parameter.

In an embodiment of the present invention, the link quality monitoringcircuit is adapted to: obtain at least one link quality parameter fromthe signal strength and noise detection circuit of the implantablemedical device corresponding to a signal strength at a receiver of theimplantable medical device; compare the obtained signal strength of thereceiver of the implantable medical device with a predetermined signalstrength threshold; and if the signal strength of the receiver is foundto exceed the signal strength threshold, determine that the present linkquality satisfies predetermined conditions.

According to an embodiment of the present invention, the link qualitymonitoring circuit may be adapted to initiate the link quality testprior to a transmission of data classified to be critical.

Moreover, the link quality monitoring circuit may be adapted to initiatethe link quality test at predetermined intervals during thecommunication session.

Further, the link quality monitoring circuit is adapted to execute apredetermined number of tests; and determine a link quality using thelink qualities of the predetermined number of tests.

In yet another embodiment of the present invention, the programmerdevice and/or the communication unit of the programmer device comprisespresentation means adapted to present the link quality and/or the linkquality margin in a visually recognizable way for an operator. Forexample, the presentation means may comprise at least two light emittingdiodes adapted to present the link quality margin in a visuallyrecognizable way for a user of the programmer device and/orcommunication unit.

Furthermore, the presentation means of the programmer device maycomprise a display screen, the control circuit of the programmer devicecomprising means for generating a graphical user interface on thedisplay screen adapted to present the link quality and/or the linkquality margin in a visually recognizable way for a user by means of atleast one distinctive colour and at least one distinctive symbol.

In accordance with another embodiment of the present invention, the linkquality monitoring circuit of the programmer device is adapted to send alink quality test instruction to a control circuit of the implantablemedical circuit instructing the control circuit to determine a linkquality of a communication link between the programmer and theimplantable medical device, the link quality test instruction furtherinstructing the control circuit to instruct a transmitter of theimplantable medical device to reduce a present signal power from aninitial signal power level according to a predetermined test protocol;obtain at least one link quality parameter at reduced signal power froma link quality parameter calculation circuit of the programmer;determine a present link quality at reduced signal power using theobtained at least one link quality parameter; and when the link qualitytest has been finished, send a stop instruction to the control circuitof the implantable medical circuit instructing the control circuit toinstruct the transmitter to return to the initial signal power level.Thereby, the link quality and/or link quality margin of the uplink canbe determined.

According to embodiments of the present invention, the link qualityand/or the link quality margin, and the link quality parameters can alsobe used to control an antenna switch. An antenna switching process maybe started, for example, when the margin is determined to be too low,i.e. when a present link quality is below a predetermined threshold. Ifthere are more than two antennas, each antenna may be activated during apredetermined period of time and the link margin may be determined foreach antenna in order to find the antenna having the best receivingconditions.

In a further embodiment of the present invention, the link qualityand/or the link quality margin, and the link quality parameters is/areused to evaluate and trigger a change of parameters such as transmitterpower, modulation method, etc.

According to a further embodiment of the present invention, in acommunication unit of the programmer having two orthogonally arrangedantennas, a test is performed when a communication link is establishedto identify which antenna providing the best transmission conditions,for example, using the monitoring or test procedures according to thedifferent aspects of the invention discussed above. The obtained linkquality parameters are also used to trigger a change of antenna and tocompare the antennas during a communication session.

As will be apparent to those skilled in the art, steps of the methods ofthe present invention, as well as preferred embodiment thereof, aresuitable to realize as a computer program or a computer readable medium.

The features that characterize the invention, both as to organizationand to method of operation, together with further objects and advantagesthereof, will be better understood from the following description usedin conjunction with the accompanying drawings. It is to be expresslyunderstood that the drawings is for the purpose of illustration anddescription and is not intended as a definition of the limits of theinvention. These and other objects attained, and advantages offered, bythe present invention will become more fully apparent as the descriptionthat now follows is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a schematically shows a programmer device and medical systemaccording to an embodiment of the present invention.

FIG. 1 b schematically shows a programmer device and medical systemaccording to another embodiment of the present invention.

FIG. 1 c schematically shows a programmer device and medical systemaccording to a further embodiment of the present invention.

FIG. 1 d schematically shows a programmer device and medical systemaccording to yet another embodiment of the present invention.

FIG. 2 schematically shows an embodiment of a link quality parametercalculating circuit of a programmer device in accordance with thepresent invention.

FIG. 3 a schematically shows an embodiment of an implantable medicaldevice in accordance with the present invention.

FIG. 3 b schematically shows another embodiment of an implantablemedical device in accordance with the present invention.

FIG. 4 schematically shows an embodiment of a link quality parametercalculating circuit of an implantable medical device in accordance withthe present invention.

FIG. 5 is a high-level description of the steps of an embodiment of themethod for continuously monitoring a link quality and/or link qualitymargin of a communication link between an implantable medical device andprogrammer device of a medical system.

FIG. 6 is a more detailed flow chart illustrating steps of the methodfor monitoring a link quality and/or link quality margin of acommunication link between an implantable medical device and programmerdevice of a medical system according to the embodiment shown in FIG. 5.

FIG. 7 is a high-level description of the steps of another embodiment ofthe method for continuously monitoring a link quality and/or linkquality margin of a communication link between an implantable medicaldevice and programmer device of a medical system.

FIG. 8 is a more detailed flow chart illustrating steps of the methodfor monitoring a link quality and/or link quality margin of acommunication link between an implantable medical device and programmerdevice of a medical system according to the embodiment shown in FIG. 7.

FIG. 9 is a high-level flow chart of an embodiment of the method fordetermining a link quality and/or link quality margin of a communicationlink between an implantable medical device and a programmer device of amedical system.

FIG. 10 is a high-level flow chart of another embodiment of the methodfor determining a link quality and/or link quality margin of acommunication link between an implantable medical device and aprogrammer device of a medical system.

FIG. 11 is a high-level flow chart of a further embodiment of the methodfor determining a link quality and/or link quality margin of acommunication link between an implantable medical device and programmerdevice of a medical system.

FIG. 12 shows diagrams illustrating the signal power at a transmitter atthe programmer and corresponding link quality and link quality marginduring a test procedure in accordance with an embodiment of the presentinvention.

FIG. 13 is flow chart of the embodiment of the method for determining alink quality and/or link quality margin of a communication link betweenan implantable medical device and programmer device of a medical systemincluding the test procedure shown in FIG. 12.

FIG. 14 shows diagrams illustrating the signal power at a transmitter atthe programmer and corresponding link quality and link quality marginduring a test procedure in accordance with a further embodiment of thepresent invention.

FIG. 15 is flow chart of the embodiment of the method for determining alink quality and/or link quality margin of a communication link betweenan implantable medical device and programmer device of a medical systemincluding the test procedure shown in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the present invention will be discussed in the contextof medical systems comprising at least an implantable pacemaker such asa bi-ventricular pacemaker, and an external or extracorporeal programmerworkstation. However, the present invention may also be implemented insystem including other implantable medical devices such as a CRT(Cardiac Resynchronization Therapy) device, or an ICD (ImplantableCardioverter Defibrillator).

With reference first to FIGS. 1 a-1 d, embodiments of the medical systemof the present invention will be described. The medical system 11comprises a programmer workstation 2 and an implanted medical device 20or 20 a (which will be described in more detail with reference to FIGS.3 a and 3 b) implanted in a patient (not shown). The programmer 2includes a control unit 4 comprising a microprocessor and acommunication unit 5, e.g. an RF telemetry circuitry for providingbi-directional RF communications with, for example, the implantedmedical device 20 or 20 a (only implantable medical device 20 shown inFIGS. 1 a-1 d, but, as the skilled man realize, the implantable medicaldevice 20 a may also be used in the system), which communication unit 5includes a transmitter 10, a receiver 12 and an antenna 13. Theprogrammer 2 may download data, commands or instructions to theimplanted medical device 20 and may receive data, commands orinstructions via uplink from the implanted medical device 20. Thecommunication unit 5 may be integrated in the programmer device 2, or,as shown in FIGS. 1 b, 1 c and 1 d, as a separate unit connected to theprogrammer device via, for example, an USB connection or adapted tocommunicate with the programmer device 2 a, 2 b, or 2 c wirelessly bymeans of a number of different technologies including short rangecommunication links including BLUETOOTH, and IEEE 802.11b, or othertypes of short-range wireless connections such as Infrared.

Further, the programmer 2 comprises a link quality monitoring circuit 14adapted to continuously monitor a link quality of a communication linkor to perform, for example, a link quality test to determine a linkquality and/or a link quality margin of a communication link between theprogrammer 2 and the implantable medical device 20. In one embodiment,the link quality monitoring circuit 14 is integrated in the control unit4. In one embodiment of the present invention, the link qualitymonitoring circuit 14 is adapted to perform a link quality test todetermine a link quality of a communication link during a communicationsession between the programmer device 2 and the implantable medicaldevice 20. In one alternative embodiment, the test is initiated prior toa transmission of data determined to be critical, i.e. after thecommunication link has been established and at the beginning of thecommunication session. According to another embodiment, the test isperformed at periodic intervals during normal communication.

The programmer 2 also comprises a memory circuit 7 which may include arandom access memory (RAM) and/or a non-volatile memory such as aread-only memory (ROM). The memory circuit may store, for example, asignal power adjusting protocol or a test protocol, a display unit ormonitor 8 for presenting information for a user by means of a graphicaluser interface (GUI) such as an indication of a link quality or a linkquality margin, and input devices (not shown), for example, a keyboardand a mouse, which enable a user to, for example, input information andcommands.

Moreover, the programmer 2 (and/or the communication unit 5, see FIGS. 1b and 1 b) includes a presentation unit 9 adapted to present orindicate, for example, a link quality or a link quality margin of acommunication link between the programmer 2 and the implantable medicaldevice 20 for a user. According to an embodiment, the presentation unit9 includes five LED (light emitting diodes) and in another embodiment adual colour LED, which will be discussed in more detail below.

Referring now to FIGS. 1 b, 1 c and 1 d, further embodiments of themedical system according to the present invention will be discussed.Like parts in the system shown in FIG. 1 a and FIGS. 1 b, 1 c and 1 dwill be denoted with the same reference numerals and descriptionsthereof will be omitted since they have been described above withreference to FIG. 1 a. In the system 11 a shown in FIG. 1 b, thecommunication unit 5 a is arranged externally from the programmer device2 a and are provided with presentation circuits 9. The communicationunit 5 a may communicate with the programmer device 2 a via a physicalconnection such as, for example, an USB connection or wirelessly bymeans of a number of different technologies including short-rangecommunication links including BLUETOOTH, and IEEE 802.11b, or othertypes of short-range wireless connections such as Infrared.

The system 11 b shown in FIG. 1 c, the programmer device 2 b comprises,in addition to the link quality monitoring circuit 14, a link qualityparameter calculation circuit 15 adapted to calculate or determine linkquality parameters during a link quality test, which link qualityparameter calculation circuit 15 will be discussed in more detail withreference to FIG. 2.

The system 11 c shown in FIG. 1 d, the programmer device 2 c comprisesthe link quality parameter calculation circuit 15 adapted to calculateor determine link quality parameters during a link quality test, whichlink quality parameter calculation circuit 15 will be discussed in moredetail with reference to FIG. 2.

As those skilled in the art will realize, there are a number ofalternative embodiments of the system that are conceivable, for example,the communication unit may be integrated in the programmer comprisingthe link quality parameter calculation circuit shown in FIG. 1 c.

Turning now to FIG. 2, an embodiment of the link quality parametercalculation circuit 15 will be discussed in more detail. In oneembodiment, the link quality parameter calculation circuit 15 comprisesan error detection circuit 16 adapted to detect at least one of thefollowing link quality parameters: forward error correction (FEC),cyclic redundancy check (CRC), or bit error rate (BER). The errordetection circuit 16 is connected to the receiver 12 and the controlunit 4 and may utilize well-known error detection techniques todetermine, for example, the bit error rate of information received byreceiver 12. Further, the error detection circuit 16 may be adapted tosample, e.g. every 100 ms, corrected errors in communication unit 5, 5 aand/or detected uncorrectable errors from the communication unit 5, 5 a.

Furthermore, the link quality parameter calculation circuit 15 includesa signal strength and noise detection circuit 17 adapted to detect asignal strength and/or a signal-to-noise ratio (SNR) connected to the tothe receiver 15 and the control unit 4 and may comprise a logarithmicamplifier which detects and filters the received RF signal and provide areceived signal strength indicator that gives a voltage proportional tothe logarithm of the signal strength at the receiver 12. Likewise, thenoise can be measured under a known period of time during which noreceived transmission. In this way the signal-to-noise ratio of thereceived signal can be measure by simple comparison of the signal andnoise samples.

Moreover, the link quality calculation circuit 15 may include a linkdelay calculation circuit 18 adapted to measure or calculate a linkdelay of the communication link. This delay can be measured bytransmitting a message using the ordinary protocol from the transmitter10 of the communication unit 5, 5 a and measure the elapsed time untilthe response from the implanted medical device 20 has been received.Another way of measuring the link delay is to measure the time requiredto read a register in the communication unit (see FIGS. 3 a and 3 b) ofthe implantable medical device 20. In this case, the measure link delaywill not include the buffering times and the delay in the processor ofthe implantable medical device 20.

The link quality parameter calculation circuit 15 may also comprise are-transmission calculation circuit 19 adapted to record or count anumber of occasions a data packet or message has been retransmitted fromthe transmitter 10 of the communication unit 5, 5 a at predeterminedintervals. In one embodiment, the number of occasions a data packet ormessage has been retransmitted from the transmitter 10 of thecommunication unit 5, 5 a more than a preset times, e.g. 10, is recordedat predetermined intervals, for example, every 100 ms.

As those skilled in the art will realize, the link quality parametercalculation circuit 15 may include one or more or all of the followingcircuits: an error detection circuit, a signal strength and noisedetection circuit, a link delay calculation circuit, and/or are-transmission calculation circuit. Moreover, there are otherconceivable parameters that can be monitored and used for thedetermination of the link quality and/or link quality margin, forexample, the presence of local RF-noise and non-telemetry signals.

In FIG. 3 a, one embodiment of the implantable medical device accordingto the present invention is shown. The implantable medical device 20,such as a bi-ventricular pacemaker, comprises a housing (not shown)being hermetically sealed and biologically inert. Normally, the housingis conductive and may, thus, serve as an electrode. The pacemaker 20 isconnectable to one or more pacemaker leads, where only two are shown inFIGS. 3 a and 3 b; namely a ventricular lead 26 a implanted in the rightventricle of the heart (not shown) and one lead 26 b implanted in acoronary vein of the left side of the heart (not shown). The leads 26 aand 26 b can be electrically coupled to the pacemaker 20 in aconventional manner. The leads 26 a, 26 b comprises one or moreelectrodes, such as a tip electrode or a ring electrode, arranged to,inter alia, measure the impedance or transmit pacing pulses for causingdepolarization of cardiac tissue adjacent to the electrode (-s)generated by a pace pulse generator 25 under influence of a controlleror control circuit 27 including a microprocessor. The controller 27controls, inter alia, pace pulse parameters such as output voltage andpulse duration.

Furthermore, the implantable medical device 20 comprises at least onesensor (not shown) adapted to sense at least one sensor signalassociated with a physiological parameter of the patient. In oneembodiment, the sensor is an activity level sensor adapted to sense anactivity level of the patient, for example, an accelerometer. The sensoris connected to a signal processing circuit 23 adapted to process sensedsignals received from the sensor.

Moreover, a storage unit 31 is connected to the controller 27, whichstorage unit 31 may include a random access memory (RAM) and/or anon-volatile memory such as a read-only memory (ROM). Storage means 31is connected to the controller 27 and the signal processing circuit 23.Detected signals from the patient's heart are processed in an inputcircuit 33 and are forwarded to the controller 27 for use in logictiming determination in known manner. The implantable medical device 20is powered by a battery (not shown), which supplies electrical power toall electrical active components of the implantable medical device 20.The implantable medical device 20 further comprises a communication unit34, for example, an RF telemetry circuitry for providing RFcommunications including a transmitter 35 and a receiver 36 connected toan antenna 37. Thereby, for example, data contained in the storage means31 can be transferred to the programmer device 2, 2 a, 2 b, or 2 c (seeFIGS. 1 a-1 d) via the communication unit 34 and a programmer interface(not shown) for use in analyzing system conditions, patient information,etc. Moreover, the implantable medical device 20 comprises a linkquality parameter calculation circuit 38 adapted to calculate ordetermine link quality parameters during a link quality test, which linkquality parameter calculation circuit 38 will be discussed in moredetail with reference to FIG. 4.

Referring to FIG. 3 b, a further embodiment of the implantable medicaldevice will be discussed. Like parts in the implantable medical deviceshown in FIG. 3 a and FIG. 3 b will be denoted with the same referencenumerals and descriptions thereof will be omitted since they have beendescribed above with reference to FIG. 3 a. The implantable medicaldevice 20 a comprises a link quality monitoring circuit 39 adapted toperform, for example, a link quality test to determine a link qualityand/or a link quality margin of a communication link between theprogrammer 2 and the implantable medical device 20 a. In one embodiment,the link quality monitoring circuit 39 is integrated in the controller27. In one embodiment of the present invention, the link qualitymonitoring circuit 39 is adapted to perform a link quality test todetermine a link quality of a communication link during a communicationsession between the programmer device 2 and the implantable medicaldevice 20 a. In one alternative embodiment, the test is initiated priorto a transmission of data determined to be critical, i.e. after thecommunication link has been established and at the beginning of thecommunication session. According to another embodiment, the test isperformed at periodic intervals during normal communication.

The link quality monitoring circuit 39 may be adapted to monitor a linkquality or perform a link quality test to determine a link quality of acommunication link during a communication session between the programmerdevice 2 b or 2 c and the implantable medical device 20 a.

Turning now to FIG. 4, an embodiment of the link quality parametercalculation circuit 38 will be discussed in more detail. In oneembodiment, the link quality parameter calculation circuit 38 comprisesan error detection circuit 40 adapted to detect at least one of thefollowing link quality parameters: forward error correction (FEC),cyclic redundancy check (CRC), or bit error rate (BER). The errordetection circuit 40 is connected to the receiver 36 and the controller27 and may utilize well-known error detection techniques to determine,for example, the bit error rate of information received by receiver 36.Further, the error detection circuit 40 may be adapted to sample, e.g.every 200 ms, corrected errors in communication unit 34 and/or detecteduncorrectable errors from the communication unit 34.

Furthermore, link quality parameter calculation circuit 38 includes asignal strength and noise detection circuit 41 adapted to detect asignal strength and/or a signal-to-noise ratio (SNR) connected to the tothe receiver 36 and the controller 27 and may comprise a logarithmicamplifier which detects and filters the received RF signal and provide areceived signal strength indicator that gives a voltage proportional tothe logarithm of the signal strength at the receiver 36. Likewise, thenoise can be measured under a known period of time during which noreceived transmission. In this way the signal-to-noise ratio of thereceived signal can be measure by simple comparison of the signal andnoise samples.

Moreover, the link quality calculation circuit 38 may include a linkdelay calculation circuit 42 adapted to measure or calculate a linkdelay of the communication link. This delay can be measured bytransmitting a message using the ordinary protocol from the transmitter35 of the communication unit 34 and measure the elapsed time until theresponse from the programmer device 2 has been received. Another way ofmeasuring the link delay is to measure the time required to read aregister in the communication unit 5, 5 a (see FIGS. 1 a-1 d) of theprogrammer device 2, 2 a, 2 c, or 2 c. In this case, the measure linkdelay will not include the buffering times and the delay in theprocessor of the control unit 4 of the programmer device 2.

The link quality parameter calculation circuit 38 may also comprise are-transmission calculation circuit 43 adapted to record or count anumber of occasions a data packet or message has been retransmitted fromthe transmitter 35 of the communication unit 34 at predeterminedintervals. In one embodiment, the number of occasions a data packet ormessage has been retransmitted from the transmitter 35 of thecommunication unit 34 more than a preset times, e.g. 10, is recorded atpredetermined intervals, for example, every 100 ms.

As the skilled person realizes, the link quality parameter calculationcircuit 38 may include one or more or all of the following circuits: anerror detection circuit, a signal strength and noise detection circuit,a link delay calculation circuit, and/or a re-transmission calculationcircuit. Moreover, there are other conceivable parameters that can bemonitored and used for the determination of the link quality and/or linkquality margin, for example, the presence of local RF-noise andnon-telemetry signals.

Referring now to FIG. 5, a high-level description of the steps of anembodiment of the method for monitoring a link quality and/or linkquality margin of a communication link between an implantable medicaldevice and programmer device of a medical system will be given.According to an embodiment, the programmer 2 b or the link qualitymonitoring circuit 14, initiates the monitoring procedure and determinesthe link quality and/or link quality margin of the communication linkbetween the programmer device 2 b and the implantable medical device 20.First, at step 50, the signal power of the transmitter 10 is reducedfrom an initial signal power according to a signal power adjustingprotocol, e.g. a predetermined step, which may be stored in the memorycircuit 7 of the programmer 2 b. Then, at step 52, at least one linkquality parameter at a present signal power level is obtained from alink quality parameter calculation circuit 38 of the implantable medicaldevice 20 and/or from a link quality parameter calculation circuit 15 ofthe programmer 2 b. This at least one link quality parameter may beobtained at predetermined intervals. In one embodiment, the link qualityparameters are measured five times per second in the communication unit5 a and ten times per second in the implantable medical device 20. Inanother embodiment, the link quality parameters are measured ten timesper second in the communication unit 5 a and ten times per second in theimplantable medical device 20. According to embodiments, at least one ofthe following parameters are obtained: error correction codes (ECC),forward error correction (FEC), cyclic redundancy check (CRC), bit errorrate (BER), signal strength, or signal-to-noise ratio (SNR), a linkdelay of the communication link, a number of re-transmissions of atleast one data packet. Thereafter, at step 54, a present link qualityusing the obtained at least one quality parameter is determined, forexample, at predetermined intervals, e.g. five times per second, in thelink monitoring circuit 14. In one embodiment, the link quality isdetermined by using the following parameters: the number of errorcorrected blocks (ECC) in the implantable medical device 20, the numberof block that could not be corrected (CRC) in the implantable medicaldevice 20. Subsequently, at step 56, the transmitter 10 of thecommunication unit 5 a of the programmer 2 b is instructed to adjust thepresent signal power based on the determined present link quality andthe protocol, which will be discussed in more detail below withreference to FIG. 6.

With reference now to FIG. 6, the method for monitoring a link qualityand/or link quality margin of a communication link between animplantable medical device and programmer device of a medical systemaccording to an embodiment will be discussed in detail. First, at step60, the signal power of the transmitter 10 is reduced from an initialsignal power according to the signal power adjusting protocol. Then, atstep 61, at least one link quality parameter at a present signal powerlevel is obtained from a link quality parameter calculation circuit 38of the implantable medical device 20 and/or from a link qualityparameter calculation circuit 15 of the programmer 2 b. This at leastone link quality parameter may be obtained at predetermined intervalsand in this embodiment the parameters: the number of error correctedblocks (ECC) in the implantable medical device 20 (hereinafter referredto as ECCi), and the number of block that could not be corrected (CRC)in the implantable medical device 20 (hereinafter referred to as CRCi)are obtained. Thereafter, at step 62, it is checked whether ECCi andCRCi, respectively, satisfy a first set of conditions, which in thisembodiment are ECCi=0 and CRCi=0 for two consecutive intervals ordeterminations. If yes, the algorithm proceeds to step 63, where thetransmitter 10 of the programmer is instructed to reduce the transmittedsignal power one step. The step size is determined by, inter alia, thesignal power adjusting protocol, and the present signal power of thetransmitter 10. The reduction of the signal power is defined in theadjusting protocol and may be performed in uniform steps or according tosuccessive decreasing steps, i.e. the lower the signal power becomes,the smaller the steps will be. On the other hand, if no, the algorithmproceeds to step 64, where it is checked whether ECCi and CRCi satisfiesa second set of conditions, which in this embodiment are ECCi>10 and0<CRCi<=40. If yes, the algorithm proceeds to step 65, where thetransmitter 10 of the programmer is instructed to increase thetransmitted signal power one step. In one embodiment, the signal poweris increased to the preceding higher signal power level according to theadjusting protocol. However, if it is found that the second set ofconditions were not satisfied, for example, if 0<ECCi<10 and CRCi=0 or0<CRCi<=40, the algorithm proceeds to step 67, where the signal power ismaintained at the present level.

In a further embodiment of the present invention, the signal power ofthe transmitter is increased or returned to the initial or maximum powerif a fourth set of predetermined conditions are satisfied, which in thisembodiment is at an antenna switch or when CRCi>40.

Referring now to FIG. 7, a high-level description of the steps ofanother embodiment of the method for monitoring a link quality and/orlink quality margin of a communication link between an implantablemedical device and programmer device of a medical system will be given.According to this embodiment, the implantable medical device 20 a or thelink quality monitoring circuit 39, initiates the monitoring procedureand determines the link quality and/or link quality margin of thecommunication link between the programmer device 2 b, 2 c and theimplantable medical device 20 a. First, at step 70, the signal power ofthe transmitter 35 is reduced from an initial signal power according toa signal power adjusting protocol, e.g. a predetermined step, which maybe stored in the storage means 31 of the implantable medical device 20a. Then, at step 72, at least one link quality parameter at a presentsignal power level is obtained from a link quality parameter calculationcircuit 38 of the implantable medical device 20 a and/or from a linkquality parameter calculation circuit 15 of the programmer 2 b, 2 c.This at least one link quality parameter may be obtained atpredetermined intervals. In one embodiment, the link quality parametersare measured five times per second in the communication unit 5 a and tentimes per second in the implantable medical device 20 a. In anotherembodiment, the link quality parameters are measured ten times persecond in the communication unit 5 a and ten times per second in theimplantable medical device 20 a. According to embodiments, at least oneof the following parameters are obtained: error correction codes (ECC),forward error correction (FEC), cyclic redundancy check (CRC), bit errorrate (BER), signal strength, or signal-to-noise ratio (SNR), a linkdelay of the communication link, a number of re-transmissions of atleast one data packet. Thereafter, at step 74, a present link qualityusing the obtained at least one quality parameter is determined, forexample, at predetermined intervals, e.g. five times per second, in thelink monitoring circuit 39. In one embodiment, the link quality isdetermined by using the following parameters: the number of errorcorrected blocks (ECC) in the implantable medical device 20 a, thenumber of block that could not be corrected (CRC) in the implantablemedical device 20 a and/or in the programmer 2 b, 2 c. Subsequently, atstep 76, the transmitter 35 is instructed to adjust the present signalpower based on the determined present link quality and the protocol,which will be discussed in more detail below with reference to FIG. 8.

With reference now to FIG. 8, the method for monitoring a link qualityand/or link quality margin of a communication link between animplantable medical device and programmer device of a medical systemaccording to an embodiment will be discussed in detail. First, at step80, the signal power of the transmitter 35 is reduced from an initialsignal power according to the signal power adjusting protocol, e.g. apredetermined step. Then, at step 81, at least one link qualityparameter at a present signal power level is obtained from a linkquality parameter calculation circuit 38 of the implantable medicaldevice 20 a and/or from a link quality parameter calculation circuit 15of the programmer 2 b, 2 c. This at least one link quality parameter maybe obtained at predetermined intervals and in this embodiment theparameters: the number of error corrected blocks (ECC) in theimplantable medical device 20 a (hereinafter referred to as ECCi), andthe number of block that could not be corrected (CRC) in the implantablemedical device 20 a (hereinafter referred to as CRCi) are obtained.Thereafter, at step 82, it is checked whether ECCi and CRCi,respectively, satisfy a first set of conditions, which in thisembodiment are ECCi=0 and CRCi=0 for two consecutive intervals. If yes,the algorithm proceeds to step 83, where the transmitter 35 of theprogrammer is instructed to reduce the transmitted signal power onestep. The step size is determined by, inter alia, the signal poweradjusting protocol, and the present signal power. The reduction of thesignal power according to the adjusting protocol may be performed inuniform steps or according to successive decreasing steps, i.e. thelower the signal power becomes, the smaller the steps will be. On theother hand, if no, the algorithm proceeds to step 84, where it ischecked whether ECCi and CRCi satisfies a second set of conditions,which in this embodiment are ECCi>0 and 0<CRCi<=40. If yes, thealgorithm proceeds to step 85, where the where the transmitter 35 of theprogrammer is instructed to increase the transmitted signal power onestep. In one embodiment, the signal power is increased to the precedinghigher signal power. However, if it is found that the second set ofconditions was not satisfied, the algorithm proceeds to step 87, wherethe signal power is maintained at the present level.

In a further embodiment of the present invention, the signal power ofthe transmitter is increased or returned to the initial or maximum powerif a fourth set of predetermined conditions are satisfied, which in thisembodiment is at an antenna switch or when CRCi>40.

With reference to FIG. 9, a description of the steps of a furtherembodiment of the method for determining a link quality and/or linkquality margin of a communication link between an implantable medicaldevice and programmer device of a medical system will be given.According to this embodiment, the programmer 2, 2 a, or 2 b or the linkquality monitoring circuit 14, initiates the test and determines thelink quality and/or link quality margin of the downlink, i.e. from theprogrammer device 2, 2 a, or 2 b to the implantable medical device 20.First, at step 90, a link quality test to determine a link quality of acommunication link during a communication session between a programmer,for example, the programmer device 2, 2 a, or 2 b, and the implantablemedical device 20 is initiated. As discussed above, the test may beinitiated prior to a transmission of data determined to be critical,i.e. after the communication link has been established and at thebeginning of the communication session between the programmer device 2,2 a, or 2 b and the implantable medical device 20. Alternatively, thetest is performed at periodic intervals during normal communication. Inone embodiment, a predetermined number of tests are executed and a linkquality using the link qualities of the predetermined number of tests isdetermined.

Then, at step 92, a signal power level of the transmitter 10 of thecommunication unit 5, 5 a of the programmer 2, 2 a, or 2 b is reducedfrom an initial signal power level according to a predetermined testprotocol. Thereafter, at step 94, at least one link quality parameter isobtained from the link quality parameter calculating circuit 38 of theimplantable medical device 20 at reduced signal power. As will bediscussed below, the link quality parameters can be obtained inaccordance to different test protocols, for example, at each stepwisereduction and/or increment of the signal power or at predeterminedinterval if the signal power is continuously reduced. In one embodiment,the signal strength, or signal-to-noise ratio (SNR) is obtained as linkquality parameters. According to embodiments, at least one of thefollowing parameters are obtained: forward error correction (FEC),cyclic redundancy check (CRC), bit error rate (BER), signal strength, orsignal-to-noise ratio (SNR), a link delay of the communication link, anumber of re-transmissions of at least one data packet.

Subsequently, at step 96, a present link quality and/or link qualitymargin is/are determined at reduced signal power using the obtained atleast one link quality parameter in the link quality monitoring circuit14. In one embodiment, the signal strength at the receiver 36 of theimplantable medical device 20 is compared with a predetermined signalstrength threshold and if the signal strength of the receiver 36 isfound to exceed the signal strength threshold, it is determined that thepresent link quality satisfies predetermined conditions. The link marginmay also, or alternatively, be determined by comparing the obtainedpresent signal strength with the predetermined signal strengththreshold. As discussed above, the link quality may be determined ateach reduced signal power level or at predetermined intervals if thesignal power is reduced continuously. Finally, at step 98, when the testis finished, the link quality monitoring circuit 14 instructs thetransmitter 10 to return to the initial signal power level.

Turning now to FIG. 10, a high-level description of the steps of afurther embodiment of the method for determining a link quality and/orlink quality margin of a communication link between an implantablemedical device and programmer device of a medical system will be given.According to this embodiment, the programmer 2 b sends, at step 100, alink quality test instruction via the communication unit 5 a to acontrol circuit or controller 27 of the implantable medical device 20instructing the control circuit 27 to determine a link quality and/orlink quality margin of the uplink of a communication link between theprogrammer 2 b and the implantable medical device 20. The test may beinitiated prior to a transmission of data determined to be critical,i.e. after the communication link has been established and at thebeginning of the communication session between the programmer device 2 band the implantable medical device 20, or, alternatively, the test isperformed at periodic intervals during normal communication. In oneembodiment, a predetermined number of tests are executed and a linkquality using the link qualities of the predetermined number of tests isdetermined.

Thereafter, at step 102, a present signal power of the transmitter 35 ofthe implantable medical device 20 is reduced from an initial signalpower level according to a predetermined test protocol. Then, at step104, at least one link quality parameter at reduced signal power isobtained from a link quality parameter calculation circuit 15 of theprogrammer 2 b. As will be discussed below, the link quality parameterscan be obtained in accordance to different test protocols, for example,at each stepwise reduction and/or increment of the signal power or atpredetermined interval if the signal power is continuously reduced. Inone embodiment, the signal strength, or signal-to-noise ratio (SNR) isobtained as link quality parameters. According to embodiments, at leastone of the following parameters are obtained: forward error correction(FEC), cyclic redundancy check (CRC), bit error rate (BER), signalstrength, or signal-to-noise ratio (SNR), a link delay of thecommunication link, a number of re-transmissions of at least one datapacket.

Subsequently, at step 106, a present link quality and/or link qualitymargin at reduced signal power using the obtained at least one linkquality parameter is determined in the link quality monitoring circuit14. In one embodiment, the signal strength at the receiver 12 of theprogrammer device 2 b is compared with a predetermined signal strengththreshold and if the signal strength of the receiver is found to exceedthe signal strength threshold, it is determined that the present linkquality satisfies predetermined conditions. The link margin may also, oralternatively, be determined by comparing the obtained present signalstrength with the predetermined signal strength threshold. As discussedabove, the link quality may be determined at each reduced signal powerlevel or at predetermined intervals if the signal power is reducedcontinuously. Finally, at step 108, when the test has been finished, thelink quality monitoring circuit 14 sends, via the communication unit 5a, a stop instruction to the control circuit 27 of the implantablemedical circuit 20 instructing the control circuit 27 to instruct thetransmitter 35 of the implantable medical device 20 to return to theinitial signal power.

Referring now to FIG. 11, a high-level description of the steps of afurther embodiment of the method for determining a link quality and/orlink quality margin of a communication link between an implantablemedical device and programmer device of a medical system will be given.According to this embodiment, the implantable medical device 20 a, orthe link quality monitoring circuit 39 of the implantable medical device20 a, initiates the test and determines the link quality and/or linkquality margin of the link uplink, i.e. from the implantable medicaldevice 20 a to the programmer device 2 b, 2 d.

First, at step 110, a link quality test to determine a link quality of acommunication link during a communication session between theprogrammer, for example, the programmer device 2 b, 2 c, and theimplantable medical device, for example, the implantable medical device20 a is initiated. As discussed above, the test may be initiated priorto a transmission of data determined to be critical, i.e. after thecommunication link has been established and at the beginning of thecommunication session between the programmer device 2 b, 2 c and theimplantable medical device 20 a. Alternatively, the test is performed atperiodic intervals during normal communication. In one embodiment, apredetermined number of tests are executed and a link quality using thelink qualities of the predetermined number of tests is determined.

Then, at step 112, a signal power level of the transmitter 35 of thecommunication unit 34 of the implantable medical device 20 a is reducedfrom an initial signal power level according to a predetermined testprotocol. Thereafter, at step 94, at least one link quality parameter isobtained from the link quality parameter calculating circuit 15 of theprogrammer device 2 b, 2 c at reduced signal power. As will be discussedbelow, the link quality parameters can be obtained in accordance todifferent test protocols, for example, at each stepwise reduction and/orincrement of the signal power or at predetermined interval if the signalpower is continuously reduced. In one embodiment, the signal strength,and/or signal-to-noise ratio (SNR) are obtained as link qualityparameters. According to embodiments, at least one of the followingparameters are obtained: forward error correction (FEC), cyclicredundancy check (CRC), bit error rate (BER), signal strength, orsignal-to-noise ratio (SNR), a link delay of the communication link, anumber of re-transmissions of at least one data packet.

Subsequently, at step 116, a present link quality and/or link qualitymargin at reduced signal power using the obtained at least one linkquality parameter is determined in the link quality monitoring circuit39. In one embodiment, the signal strength at the receiver 12 of theprogrammer device 20 a is compared with a predetermined signal strengththreshold and if the signal strength of the receiver 12 is found toexceed the signal strength threshold, it is determined that the presentlink quality satisfies predetermined conditions. The link margin mayalso, or alternatively, be determined by comparing the obtained presentsignal strength with the predetermined signal strength threshold. Asdiscussed above, the link quality may be determined at each reducedsignal power level or at predetermined intervals if the signal power isreduced continuously. Finally, at step 118, when the test is finished,the controller 27 or the link quality monitoring circuit 39 instructsthe transmitter 35 to return to the initial signal power level.

With respect now to FIGS. 12, 13, 14, and 15, tests procedures inaccordance with embodiment of the present invention will be discussed.The test procedures will be described with reference to an embodimentwhere the link quality monitoring circuit 14 is arranged in theprogrammer device 2, 2 a, 2 b, the downlink is tested and the at leastone link quality parameter is obtained from the implantable medicaldevice 20. In this exemplifying case, the link quality parameter is thesignal strength.

First, referring to FIGS. 12 and 13, an embodiment where the signalpower is reduced step-wise will be discussed. Initially, at step 130,the signal power is reduced from an initial signal power S_initial to afirst test signal power S1 at a point of time t1. As can be seen in FIG.12, the signal power of the transmitter 10 is reduced stepwise atregular intervals, which is performed in accordance with a predeterminedtest protocol including the step size and the time intervals. Then, atstep 132, the link quality is determined at this reduced signal powerS1. Thereafter, at step 134, the present link quality is compared withpredetermined conditions, which, in one embodiment, is a predeterminedlink quality threshold and it is determined whether the present linkquality exceeds the threshold. If the link quality exceeds thethreshold, the link quality is determined to be adequate and thealgorithm returns to step 130 where the signal power is reduced afurther step, from S1 to S2 at the point of time t2. This procedure isrepeated until, at step 134, it is determined that the present linkquality is not adequate, i.e. is below the predetermined threshold. Inthis exemplifying case, the link quality is determined to be adequate att2 and t3, i.e. the signal strength exceeds the predetermined threshold.At t4, the present link quality is below the threshold and the algorithmproceeds to step 136 where the test is terminated and the signal poweris returned to the initial level. The link quality at the initial signalpower may be determined when the signal power has returned to theinitial level or before the initial signal power has been reduced at thebeginning of the test. The link quality margin may also be determined.

In one embodiment, the link quality margin is determined as thedifference between the signal strength at the initial signal power andthe signal strength being below the threshold. In another embodiment ofthe present invention, the link quality margin is determined as thedifference between the signal strength at the initial signal power andthe signal strength at the preceding signal power level. As will bediscussed below, the link quality and/or link quality margin may beindicated or presented for a used using, for example, light emittingdiodes arranged at the programmer device 2, 2 a, 2 b, or 2 c, and/or atthe communication unit 5, 5 a. Alternative, the link quality and/or linkquality margin may be presented at a display means 8 of programmer 2, 2a, 2 b, or 2 c using a graphical user interface. The link quality marginmay also be determined by using this comparison.

Referring to FIGS. 14 and 15, an embodiment where the signal power isreduced continuously during a period of time t_test will be discussed.

First, at step 150, the continuous reduction of the signal power from aninitial signal power S_initial is initiated. As can be seen in FIG. 14,the signal power of the transmitter 10 is reduced continuously during atest period t_test, which is performed in accordance with apredetermined test protocol including the length of the test period andthe reduction rate. Then, at step 152, the link quality is determinedafter a first time interval t5. Thereafter, at step 154, the presentlink quality is compared with predetermined conditions, which, in oneembodiment, is a predetermined link quality threshold and it isdetermined whether the present link quality exceeds the threshold. Ifthe link quality exceeds the threshold, the link quality is determinedto be adequate and the algorithm returns to step 150 and the reductionof the signal power is continued. This procedure is repeated until, atstep 154, it is determined that the present link quality is notadequate, i.e. is below the predetermined threshold. In thisexemplifying case, the link quality is determined to be adequate at t6and t7. At t8, the present link quality is below the threshold and thealgorithm proceeds to step 156 where the test is terminated and thesignal power is returned to the initial level. The link quality at theinitial signal power may be determined when the signal power hasreturned to the initial level or before the initial signal power hasbeen reduced at the beginning of the test. The link quality margin mayalso be determined.

In one embodiment, the link quality margin is determined as thedifference between the signal strength at the initial signal power andthe signal strength being below the threshold. In another embodiment,the link quality margin is determined as the difference between thesignal strength at the initial signal power and the signal strength atthe preceding signal power level. As will be discussed below, the linkquality and/or link quality margin may be indicated or presented for aused using, for example, light emitting diodes arranged at theprogrammer device 2, 2 a, 2 b, or 2 c, and/or at the communication unit5, 5 a. Alternative, the link quality and/or link quality margin may bepresented at a display means 8 of programmer 2, 2 a, 2 b, or 2 c using agraphical user interface. In this illustrated case, the test wasterminated before the test period had elapsed since the link qualityparameter was found to be below the threshold. According to analternative, the test can be terminated after the test period haselapsed regardless the level of the link quality.

As discussed above, the link quality and/or link quality margin can beindicated or presented for a user at a display of the programmer deviceor by means of light emitting means arranged at the programmer deviceand/or communication unit.

In one embodiment, the determination of whether there is sufficientmargin to maintain an adequate RF link is used for the link qualityindicator. The link quality indication has two states: link OK and linkNOK (not OK). One dual colour LED can be used where the state link OK isindicated with a green light of the LED and the link state link NOK isindicated with a red light. In an alternative embodiment, a singlecolour LED with different flashing codes are used; where the state linkOK is indicates with the LED being continuously lit and the state linkNOK is indicated with a flashing light of the LED.

According to another embodiment, the link quality and/link qualitymargin is indicated with a number of LEDs, for example, five LEDs. A bigmargin (or a very good link) may be indicated with all five LEDs beinglit. Four LEDs are lit when some link margin exists (or when the link isgood). Three LEDs are lit when the margin is very little (when the linkis OK). Two LEDs are lit when the link margin is below predeterminedconditions (the link is degraded). One LED is lit when the far belowpredetermined conditions (the link is very degraded).

In another embodiment of the present invention, the link quality and/orlink quality margin is determined by means of the following parameters:forward error correction, cyclic redundancy check, the number ofre-transmissions, the signal strength and the link delay. In this case,five LEDs are used at the programmer and five LEDs at the communicationunit. Each LED has a set of limit parameter values, one value for eachlink quality parameter. As long as all parameters exceed respectivelimit, the LED is lit. As soon as at least one of the parameters isbelow the respective limit, the LED will be switched off. The limitvalues may be chosen so that a big margin (or a very good link) isindicated with all five LEDs being lit. Four LEDs are lit when some linkmargin exists (or when the link is good). Three LEDs are lit when themargin is very little (when the link is OK). Two LEDs are lit when thelink margin is below predetermined conditions (the link is degraded).One LED is lit when the far below predetermined conditions (the link isvery degraded).

According to yet another embodiment of the present invention, linkquality and/or the link quality margin is presented in a visuallyrecognizable way for an operator by means of at least one distinctivecolour and at least one distinctive symbol at a display screen 8,wherein a control circuit 4 of the programmer device 2, 2 a, 2 b, or 2 dcomprises means for generating a graphical user interface on the displayscreen adapted to present the symbol (-s) and/or the distinctive colour.For example, a green and positive symbol (e.g. a star or a shining sun)may indicate a big margin, a yellow question mark may indicate a smallmargin, and a red cross may indicate a “negative margin” (i.e. a presentlink quality below the threshold).

In a certain embodiment, the green and positive symbol may indicate atransmission condition where all data is transmitted without errors(e.g. ECCi=0 and CRCi=0), the a yellow question mark may indicate thatdata is transmitted, but error corrections and retransmissions arenecessary and the data is transmitted correctly despite errors andcorrections in the received signals (e.g. ECCi>0 and 0<CRCi<=40), and ared cross may indicate that the received data contains too much errorsto allow a reconstruction of the information (e.g. CRCi>40).

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, therefore, that other expedientsknown to those of skill in the art or disclosed herein may be employedwithout departing from the invention as defined by the appended claims.It is therefore understood that the invention may be practiced otherwisethan is specifically described without departing from the scope of thepresent invention.

The invention claimed is:
 1. A medical system comprising: an implantablemedical device configured for implantation in a subject, saidimplantable medical device comprising a receiver; an external programmerdevice configured for extracorporeal communication with said implantablemedical device in the subject, said external programmer devicecomprising a transmitter that establishes a wireless communication linkwith said receiver of said implantable medical device; a link qualitymonitoring circuit in said external programmer configured to determine alink quality of said communication link during a communication sessionbetween said external programmer device and said implantable medicaldevice; a link quality parameter calculation unit, located in eithersaid external programmer or said implantable medical device, configuredto calculate a link quality parameter that represents a quality of saidcommunication link in said communication session; and said link qualitymonitoring circuit being configured to instruct said transmitter of saidexternal programmer to reduce a signal power of a signal transmitted tosaid receiver from an initial signal power level according to apredetermined signal power adjusting protocol, and to obtain said linkquality parameter from said link quality parameter calculation unit, andto determine a present link quality using said at least one link qualityparameter, and to instruct said transmitter to adjust the reduced signalpower level dependent on said present link quality and said signal poweradjusting protocol, and to instruct said transmitter to return to saidinitial signal power level if said link quality parameter satisfies afirst set of predetermined conditions.
 2. A medical system as claimed inclaim 1 wherein said link quality monitoring circuit is configured toinstruct said transmitter to reduce said signal power level from saidpresent signal power level according to said signal power adjustingprotocol, if said link quality parameter satisfies a second set ofpredetermined conditions, and to instruct said transmitter to increasesaid signal power level from said present signal power level accordingto said signal power adjusting protocol, if said link quality parametersatisfies a third set of predetermined conditions.
 3. A medical systemas claimed in claim 2 wherein said link quality monitoring circuit isconfigured to instruct said transmitter to maintain said present signalpower level at said present signal power level if said link qualityparameters satisfies a fourth set of predetermined conditions.
 4. Amedical system as claimed in claim 3 wherein said transmitter isconfigured to transmit data in blocks, and wherein said externalprogrammer device comprises an antenna connected to said transmitterthat transmits said data in said blocks to said receiver of saidimplantable medical device, and wherein said first set of conditionscomprises a number of said blocks containing errors that could not becorrected in said implantable medical device (CRCi) being higher than40, or a change of said antenna of said external programmer device, andwherein said second set of conditions comprises a number of errorcorrected blocks in said implantable medical device (ECCi) being equalto zero and CRCi being equal to zero for two consecutive determinationsof said link quality parameter, and wherein said third set of conditionscomprises ECCi being higher than 10 and CRCi being higher than zero andlower than 40, and wherein said fourth set of conditions comprises ECCibeing lower than 10 and CRCi being equal to or greater than zero andless than
 40. 5. A medical system as claimed in claim 1 wherein saidlink quality monitoring circuit is configured to determine said linkquality in a link quality test, and to instruct said transmitter toreturn to said initial signal power level when said link quality test isconcluded.
 6. A system as claimed in claim 1 wherein said link qualityparameter calculation unit calculates said link quality parameter fromthe group of link quality parameters consisting of signal strength andsignal-to-noise ratio.
 7. A system as claimed in claim 1 wherein saidimplantable medical device comprises a transmitter that transmits aresponse signal upon said receiver of said implantable medical devicereceiving the signal transmitted from said transmitter of said externalprogrammer device, and wherein said link quality parameter calculationunit is configured to calculate a link delay of said communication linkdependent on a response received by said external programmer devicefollowing transmission of a signal from said external programmer deviceto said implantable medical device, or to read a register in saidexternal programmer device.
 8. A system as claimed in claim 1 whereinsaid transmitter is configured to transmit data to said implantablemedical device, and wherein said monitoring unit is configured toidentify when data to be transmitted by said transmitter are criticaldata, and to initiate a link quality test, wherein said link quality isdetermined, prior to transmission of said data classified as critical.9. A system as claimed in claim 1 wherein said programmer devicecomprises a presentation unit configured to provide a visual indicationof said link quality or a link quality margin.
 10. A system as claimedin claim 9 wherein said presentation unit comprises two light emittingdiodes operable by said link quality monitoring circuit to provide avisual indication of said link quality or said link quality margin. 11.A system as claimed in claim 9 wherein said presentation unit is adisplay screen, and wherein said programmer device comprises a controlunit control unit connected to said display screen that generates agraphical user interface at said display screen that is a visualindicator of said link quality or said link quality margin.
 12. A systemas claimed in claim 9 wherein said link quality monitoring circuit isconfigured to determine a quality level of said link quality or saidlink quality margin, wherein a first quality level represents a linkquality above a predetermined upper level above a threshold, a secondquality level represents a link quality between said predetermined upperlevel and said threshold, and a third quality level represents a linkquality below said threshold, and wherein said presentation unitcomprises a display screen, and wherein said programmer device comprisesa control circuit connected to said display screen, said control circuitbeing configured to generate a graphical user interface at said displayscreen that indicates said first quality level with a first color and afirst symbol, and that indicates said second quality level with a secondcolor and a second symbol, and that indicates said third quality levelwith a third color and a third symbol.
 13. A medical system comprising:an implantable medical device configured for implantation in a subject,said implantable medical device comprising a transmitter; an externalprogrammer device configured for extracorporeal communication with saidimplantable medical device in the subject, said external programmerdevice comprising a receiver, and said transmitter in said implantablemedical device being configured to establish a wireless communicationlink with said receiver of said external programmer; a link qualitymonitoring circuit in said implantable medical device configured todetermine a link quality of said communication link during acommunication session between said external programmer and saidimplantable medical device; a link quality parameter calculation unit,located in either said external programmer or said implantable medicaldevice, configured to calculate a link quality parameter that representsa quality of said communication link in said communication session; andsaid link quality monitoring circuit being configured to instruct saidtransmitter of said implantable medical device to reduce a signal powerof a signal transmitted to said receiver from an initial signal powerlevel according to a predetermined signal power adjusting protocol, andto obtain said link quality parameter from said link quality parametercalculation unit, and to determine a present link quality using said atleast one link quality parameter, and to instruct said transmitter toadjust the reduced signal power level dependent on said present linkquality and said signal power adjusting protocol, and to instruct saidtransmitter to return to said initial signal power level if said linkquality parameter satisfies a first set of predetermined conditions. 14.A medical system as claimed in claim 13 wherein said link qualitymonitoring circuit is configured to instruct said transmitter to reducesaid signal power level from said present signal power level accordingto said signal power adjusting protocol, if said link quality parametersatisfies a second set of predetermined conditions, and to instruct saidtransmitter to increase said signal power level from said present signalpower level according to said signal power adjusting protocol, if saidlink quality parameter satisfies a third set of predeterminedconditions.
 15. A medical system as claimed in claim 14 wherein saidlink quality monitoring circuit is configured to instruct saidtransmitter to maintain said present signal power level at said presentsignal power level if said link quality parameters satisfies a fourthset of predetermined conditions.
 16. A medical system as claimed inclaim 15 wherein said transmitter is configured to transmit data inblocks, and wherein said implantable medical device comprises an antennaconnected to said transmitter that transmits said data in said blocks tosaid receiver of said external programmer device, and wherein said firstset of conditions comprises a number of said blocks containing errorsthat could not be corrected in said implantable medical device (CRCi)being higher than 40, or a change of said antenna of said implantablemedical device, and wherein said second set of conditions comprises anumber of error corrected blocks in said implantable medical device(ECCi) being equal to zero and CRCi being equal to zero for twoconsecutive determinations of said link quality parameter, and whereinsaid third set of conditions comprises ECCi being higher than 10 andCRCi being higher than zero and lower than 40, and wherein said fourthset of conditions comprises ECCi being lower than 10 and CRCi beingequal to or greater than zero and less than
 40. 17. A medical system asclaimed in claim 13 wherein said link quality monitoring circuit isconfigured to determine said link quality in a link quality test, and toinstruct said transmitter to return to said initial signal power levelwhen said link quality test is concluded.
 18. A system as claimed inclaim 13 wherein said link quality parameter calculation unit calculatessaid link quality parameter from the group of link quality parametersconsisting of signal strength and signal-to-noise ratio.
 19. A system asclaimed in claim 13 wherein said external programmer device comprises atransmitter that transmits a response signal upon said receiver of saidexternal programmer device receiving the signal transmitted from saidtransmitter of said implantable medical device, and wherein said linkquality parameter calculation unit is configured to calculate a linkdelay of said communication link dependent on a response received bysaid implantable medical device following transmission of a signal fromsaid implantable medical device to said external programmer device, orto read a register in said implantable medical device.
 20. A system asclaimed in claim 13 wherein said transmitter is configured to transmitdata to said external programmer device, and wherein said monitoringunit is configured to identify when data to be transmitted by saidtransmitter are critical data, and to initiate a link quality test,wherein said link quality is determined, prior to transmission of saiddata classified as critical.
 21. A system as claimed in claim 13 whereinsaid programmer device comprises a presentation unit configured toprovide a visual indication of said link quality or a link qualitymargin.
 22. A system as claimed in claim 21 wherein said presentationunit comprises two light emitting diodes operable by said link qualitymonitoring circuit to provide a visual indication of said link qualityor said link quality margin.
 23. A system as claimed in claim 21 whereinsaid presentation unit is a display screen, and wherein said programmerdevice comprises a control unit control unit connected to said displayscreen that generates a graphical user interface at said display screenthat is a visual indicator of said link quality or said link qualitymargin.
 24. A system as claimed in claim 21 wherein said link qualitymonitoring circuit is configured to determine a quality level of saidlink quality or said link quality margin, wherein a first quality levelrepresents a link quality above a predetermined upper level above athreshold, a second quality level represents a link quality between saidpredetermined upper level and said threshold, and a third quality levelrepresents a link quality below said threshold, and wherein saidpresentation unit comprises a display screen, and wherein saidprogrammer device comprises a control circuit connected to said displayscreen, said control circuit being configured to generate a graphicaluser interface at said display screen that indicates said first qualitylevel with a first color and a first symbol, and that indicates saidsecond quality level with a second color and a second symbol, and thatindicates said third quality level with a third color and a thirdsymbol.
 25. A method for operating a medical system comprising animplantable medical device configured for implantation in a subject,said implantable medical device comprising a receiver, and an externalprogrammer device configured for extracorporeal communication with saidimplantable medical device in the subject, said external programmerdevice comprising a transmitter, said method comprising the steps of:establishing a wireless communication link between said transmitter ofsaid external programmer device and with said receiver of saidimplantable medical device; in a link quality monitoring circuit in saidexternal programmer, automatically determining a link quality of saidcommunication link during a communication session between said externalprogrammer device and said implantable medical device; in a link qualityparameter calculation unit, located in either said external programmeror said implantable medical device, automatically calculating a linkquality parameter that represents a quality of said communication linkin said communication session; and from said link quality monitoringcircuit, automatically instructing said transmitter of said externalprogrammer device to reduce a signal power of a signal transmitted tosaid receiver from an initial signal power level according to apredetermined signal power adjusting protocol, and to obtain said linkquality parameter from said link quality parameter calculation unit, andto determine a present link quality using said at least one link qualityparameter, and to instruct said transmitter to adjust the reduced signalpower level dependent on said present link quality and said signal poweradjusting protocol, and to instruct said transmitter to return to saidinitial signal power level if said link quality parameter satisfies afirst set of predetermined conditions.
 26. A method as claimed in claim25 comprising, from said link quality monitoring circuit, instructingsaid transmitter to reduce said signal power level from said presentsignal power level according to said signal power adjusting protocol, ifsaid link quality parameter satisfies a second set of predeterminedconditions, and to instruct said transmitter to increase said signalpower level from said present signal power level according to saidsignal power adjusting protocol, if said link quality parametersatisfies a third set of predetermined conditions.
 27. A method asclaimed in claim 26 comprising, from said link quality monitoringcircuit, instructing said transmitter to maintain said present signalpower level at said present signal power level if said link qualityparameters satisfies a fourth set of predetermined conditions.
 28. Amethod for operating a medical system comprising an implantable medicaldevice configured for implantation in a subject, said implantablemedical device comprising a transmitter and an external programmerdevice configured for extracorporeal communication with said implantablemedical device in the subject, said external programmer devicecomprising a receiver, said method comprising the steps of: establishinga wireless communication link between said receiver of said externalprogrammer device and said transmitter of said implantable medicaldevice; in a link quality monitoring circuit in said implantable medicaldevice, automatically determining a link quality of said communicationlink during a communication session between said external programmerdevice and said implantable medical device; in a link quality parametercalculation unit, located in either said external programmer or saidimplantable medical device, automatically calculating a link qualityparameter that represents a quality of said communication link in saidcommunication session; and from said link quality monitoring circuit,instructing said transmitter of said implantable medical device toreduce a signal power of a signal transmitted to said receiver from aninitial signal power level according to a predetermined signal poweradjusting protocol, and to obtain said link quality parameter from saidlink quality parameter calculation unit, and to determine a present linkquality using said at least one link quality parameter, and to instructsaid transmitter to adjust the reduced signal power level dependent onsaid present link quality and said signal power adjusting protocol, andto instruct said transmitter to return to said initial signal powerlevel if said link quality parameter satisfies a first set ofpredetermined conditions.